there is an easier (in my opinion) way to do it...just did it an hour ago..worked like a charm
I AM NOT TAKING CREDIT FOR THIS, JUST PASSING IT ALONG
Just flashed cwm touch for T-Mobile. Looks pretty nice. Its available in from rom manager or if you dont wanna pay for it do this
Download the recovery image from here
http://www.clockworkmod.com/rommanager (tmobile Galaxy S2)
Rename it to recovery.img and place it on your sdcard(internal) so it should be at /sdcard/recovery.img
plug phone into computer and get into adb shell from terminal (must have adb working)
then type this: dd if=/sdcard/recovery.img of=/dev/block/mmcblk0p22
IF you dont have adb working on your computer you can download terminal emulator from android market and do it from your phone. Same instructions as above.
place recovery.img on sdcard(/sdcard/recovery.img)
open terminal emulator and type: su (allow superuser access if it ask you)
then type: dd if=/sdcard/recovery.img of=/dev/block/mmcblk0p22
make sure usb debugging is checked also.
Credit for these instructions belongs to Da_G